Another day at the wide-open Open, where nothing has gone as predicted except the looming presence of a Northern Irish golfer at the top of the leaderboard.

Alas for the soothsayers and those in search of an orderly life, that golfer is not the mop-top kid from Holywood, Rory McIlroy, but the rotund gent from Dungannon, Darren Clarke.

Wild weather is forecast for the weekend at Royal St George's but the two friends will relish the challenge of winning another major championship for the world's smallest golfing superpower. At the very least they know they have a chance of victory, which is more than can be said of Luke Donald and Lee Westwood, the world's No1 and No2 golfers. The two Englishmen were tipped by many to win their first major but instead were homeward bound. Westwood missed the cut by one shot, Donald by three.

What a contrast their fortunes made with Clarke, who spent the preliminaries at Royal St George's fielding questions about McIlroy and the first two days of the main event reminding the world there is more than one golfer from his neck of the woods. A first-round 68 was a fine effort from the 42-year-old but his 68 on Friday was a real beauty and vaulted him to the top at halfway, on four under, alongside the under-rated American Lucas Glover.

"There is an awful long way to go and the course is playing quite tough, so the tournament is still wide open for an awful lot of players," Clarke said. He was right about that. Martin Kaymer and Charl Schwartzel, the US PGA champion and the Masters winner, were prominent in the cavalry charge behind the leaders. As was the young amateur Tom Lewis, who followed his opening day 65 with a very respectable 74, That was good enough for a one-under total of 139, though it did not quite match up to the 20-year-old's expectations. Still, at least he gets to play at the weekend of the 2011 Open – which is more than can be said of Graeme McDowell and Ian Poulter, two more illustrious names who missed the cut – and he got to watch his playing partner Tom Watson make a hole-in-one at the par-three 6th.

McIlroy is one shot further back after a one-under 69, the highlight of which was a stunning greenside bunker shot on the final hole – from a plugged lie and over a lip that must have looked the north face of the Eiger. He rolled in a 10-footer for par. "I put a lot of pressure on me to hole that putt, and it makes me feel pretty good going into the weekend," he said.

The US Open champion was not alone. Indeed, with the 72 players who made the cut within seven shots of the lead, all of them will believe victory is possible, and of those perhaps as many as half are right. A man could lose a wardrobe of shirts backing the accuracy of weather forecasts but barring another Michael Fish moment the Kent coast is likely to be battered by wind and rain for most of Saturday, in which case hold on to your hat, your umbrella and your temper.

"It's going to be a battle," predicted Kaymer after his day was done. If so, then who is up for the fight?

Clarke certainly looks and sounds like he is, even if he is some way removed from the consistently world-class golfer he was a decade ago. Yet there are some things that have not been stripped from the Northern Irishman's armoury. He can still win golf tournaments – as he did in Spain earlier this year – and he can still play in bad weather, as befits someone who grew up playing seaside golf and spends most of his practice time at Royal Portrush, the legendary links on the Antrim coast.

"I've been doing a lot of practising in bad weather because that's usually what we get in Portrush," he said. "Actually, it's not always that bad, but it has certainly been the case that I've been getting used to playing in conditions like this over the winter. Hopefully, it will stand me in good stead."

It will. And so will the quality of his golf. It is not for nothing that Clarke is often mentioned in the same sentence as Tiger Woods and young Mr McIlroy when the subject of great ball-striking comes up. You don't need the man from the Massachusetts Institute of Technology to tell you that a purely struck ball will be hard to knock off course, wind or no wind.

However there must be a question about his mentality – will he maintain his composure when, as will inevitably happen, something goes wrong?

The same applies to every other contender, including Dustin Johnson, on two under par, and Phil Mickelson, one shot further back. The two Americans are unquestionably talented enough to win this tournament, but how will they fare in a gale?

Johnson hits the ball skyscraper high, which is not ideal (to say the least) and Mickelson has a long and mostly inglorious record at the Open. Suffice to say, the weather in his home town of San Diego is a tad different from what lies ahead. But hope springs eternal for sunny Phil. "Historically, I have not played well in wind and rain but I welcome the challenge." He better had. And so will everyone else.